The present invention relates to a non-linear digital emphasis circuit which is applied to a video signal recording circuit such as a digital circuit of a VTR, for example.
In a conventional VTR, a non-linear pre-emphasis circuit is provided before an FM modulator for frequency modulating a video signal. The non-linear pre-emphasis circuit increases the emphasis amount in the region at a low level where the noise is conspicuous and decreases the emphasis amount in the region at a high level where the noise is inconspicuous in case of emphasizing the high frequency component of the video signal. A conventional non-linear pre-emphasis circuit may comprise: a pre-emphasis circuit using L (inductance) and C (capacitance) and R (resistance); and a limiter in which two diodes are connected in parallel so that their polarities are opposite.
However, a conventional analog emphasis circuit has the following drawbacks. First, an error of the pre-emphasis characteristic occurs due to a variation in values of the circuit elements and a change in pre-emphasis characteristic occurs due to a time change of the circuit elements, so that it is necessary to adjust the pre-emphasis characteristic. Secondly, since L and C parts are used and the above-mentioned adjustment is needed, the circuit scale becomes large, so that this makes it impossible to construct an integrated circuit.